Systems and methods for optical sensing with angled filters

ABSTRACT

Disclosed is a device for optical sensing, comprising: a display comprising a transparent substrate and a plurality of light emitters disposed above the transparent substrate; a transparent cover layer disposed above the display, wherein a top surface of the transparent cover layer provides an input surface for sensing an input object; and, an angled filter disposed below the transparent substrate of the display, wherein the angled filter is configured to allow light within a tolerance angle of an acceptance angle to pass through the angled filter, wherein the acceptance angle is centered around a non-zero angle relative to a normal of the input surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority of U.S. Provisional PatentApplication Ser. No. 62/534,186, filed Jul. 18, 2017, which is herebyincorporated by reference in its entirety.

BACKGROUND

Object imaging is useful in a variety of applications. By way ofexample, biometric recognition systems image biometric objects forauthenticating and/or verifying users of devices incorporating thebiometric recognition systems. Biometric imaging provides a reliable,non-intrusive way to verify individual identity for recognitionpurposes. Various types of sensors may be used for biometric imaging.

SUMMARY

One embodiment provides a device for optical sensing, comprising: adisplay comprising a transparent substrate and a plurality of lightemitters disposed above the transparent substrate; a transparent coverlayer disposed above the display, wherein a top surface of thetransparent cover layer provides an input surface for sensing an inputobject; and an angled filter disposed below the transparent substrate ofthe display, wherein the angled filter is configured to allow lightwithin a tolerance angle of an acceptance angle to pass through theangled filter, wherein the acceptance angle is centered around anon-zero angle relative to a normal of the input surface.

Another embodiment provides an optical sensor, comprising: an imagesensor array comprising a plurality of pixels; and an angled filterdisposed above the image sensor array, the angled filter comprising aplurality of light collimating apertures and light blocking material,wherein the angled filter is configured to allow light reflected from aninput surface towards the image sensor array that is within a toleranceangle of an acceptance angle to pass through the angled filter, whereinthe acceptance angle is centered around a non-zero angle relative to anormal of the input surface.

Yet another embodiment provides a method of forming an optical element,the method comprising: providing a bundle of optical fibers in whicheach of the optical fibers includes a core surrounded by a lightabsorbing material; slicing the bundle with a plurality of cuts to forman angled filter, wherein each cut of the plurality of cuts is parallelto each other cut and is between 0 and 90 degrees relative to an axis ofthe optical fibers; and forming an optical sensor that includes theangled filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of an electronic device thatincludes an optical sensor and a processing system, according to anembodiment of the disclosure.

FIG. 2 illustrates an example of an electronic device, which includes acover layer over a display, according to an embodiment of thedisclosure.

FIG. 3 depicts an optical sensor in accordance with some embodiments ofthe disclosure.

FIG. 4 depicts example reflectance in an optical fingerprint sensor, inaccordance with some embodiments.

FIG. 5 is a graph illustrating example valley reflectance R_(Valley)plotted against incident angle of incoming light, according to oneembodiment.

FIG. 6 is a graph illustrating example ridge reflectance R_(Ridge)plotted against incident angle of incoming light, according to oneembodiment.

FIGS. 7-8 are graphs illustrating example ridge/valley contrast,according to some embodiments.

FIGS. 9A-9B illustrate examples of an optical sensor with a collimatorfilter layer according to an embodiment of the disclosure.

FIG. 10 depicts an example of an optical fingerprint sensor stack-uphaving an angled collimator, according to one embodiment.

FIG. 11A depicts an example structure and method of manufacturing anangled collimator using a fiber, in accordance with some embodiments.

FIG. 11B depicts a flow diagram of forming an optical element, accordingto one embodiment.

FIG. 12 depicts an example structure and method of manufacturing anangled collimator using stacked aperture layers, in accordance with someembodiments.

FIG. 13 depicts an example structure and method of manufacturing anangled collimator using stacked aperture layers and microlenses, inaccordance with some embodiments

FIGS. 14A-14B show examples in which an angular filter (such as one ofthe angled collimators described above) can be used outside of anydisplay area in connection with discrete light source for illuminatingthe sensing region, according to various embodiments.

FIG. 15 shows an example in which an angular filter can be used togenerate a collimated backlight for illuminating a sensing region,according to one embodiment.

FIG. 16 depicts an embodiment in which a screen protection film isincluded over a cover layer.

FIGS. 17-18 are graphs illustrating example ridge/valley contrast of asensor device that includes a protection film, according to someembodiments.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the following detaileddescription.

As described in greater detail herein, disclosed is an optical sensorincluding an angled collimator structure that allows incident light of apredetermined, non-zero acceptance angle to pass through the collimatorstructure to reach image sensor elements. In the context of fingerprintsensing, the non-zero angle is optimized relative to a vertical axis(i.e., relative to normal of a sensing surface), such that improvedridge/valley contrast is achieved.

Turning to the drawings, FIG. 1 is a block diagram of an example of anelectronic device 100 that includes an optical sensor 102 and aprocessing system 104, according to an embodiment of the disclosure.

By way of example, basic functional components of the electronic device100 utilized during capturing, storing, and validating a biometric matchattempt are illustrated. The processing system 104 may includeprocessor(s) 106, memory 108, template storage 110, operating system(OS) 112, and power source(s) 114. Processor(s) 106, memory 108,template storage 110, and operating system 112 may be connectedphysically, communicatively, and/or operatively to each other directlyor indirectly. The power source(s) 114 may be connected to the variouscomponents in processing system 104 to provide electrical power asnecessary.

As illustrated, the processing system 104 may include processingcircuitry including one or more processor(s) 106 configured to implementfunctionality and/or process instructions for execution withinelectronic device 100. For example, processor(s) 106 executeinstructions stored in memory 108 or instructions stored on templatestorage 110 to normalize an image, reconstruct a composite image,identify, verify, or otherwise match a biometric object, or determinewhether a biometric authentication attempt is successful. Memory 108,which may be a non-transitory, computer-readable storage medium, may beconfigured to store information within electronic device 100 duringoperation. In some embodiments, memory 108 includes a temporary memory,an area for information not to be maintained when the electronic device100 is turned off. Examples of such temporary memory include volatilememories such as random access memories (RAM), dynamic random accessmemories (DRAM), and static random access memories (SRAM). Memory 108may also maintain program instructions for execution by the processor(s)106.

Template storage 110 may comprise one or more non-transitorycomputer-readable storage media. In the context of a fingerprint sensordevice or system, the template storage 110 may be configured to storeenrollment views or image data for fingerprint images associated with auser's fingerprint, or other enrollment information, such as templateidentifiers, enrollment graphs containing transformation informationbetween different images or view, etc. More generally, the templatestorage 110 may store information about an input object. The templatestorage 110 may further be configured for long-term storage ofinformation. In some examples, the template storage 110 includesnon-volatile storage elements. Non-limiting examples of non-volatilestorage elements include magnetic hard discs, solid-state drives (SSD),optical discs, floppy discs, flash memories, or forms of electricallyprogrammable memories (EPROM) or electrically erasable and programmable(EEPROM) memories, among others.

The processing system 104 may also host an operating system (OS) 112.The operating system 112 may control operations of the components of theprocessing system 104. For example, the operating system 112 facilitatesthe interaction of the processor(s) 106, memory 108, and templatestorage 110.

According to some embodiments, the processor(s) 106 implements hardwareand/or software to obtain data describing an image of an input object.In some implementations, the processor(s) 106 may also determine whetherthere is a match between two images, e.g., by aligning two images andcompare the aligned images to one another. The processor(s) 106 may alsooperate to reconstruct a larger image from a series of smaller partialimages or sub-images, such as fingerprint images when multiple partialfingerprint images are collected during a biometric process, such as anenrollment or matching process for verification or identification.

The processing system 104 may include one or more power source(s) 114 toprovide power to the electronic device 100. For example, the powersource(s) 114 may provide power to one or more of the components of theprocessing system 104 and/or to the optical sensor 102. In someimplementations, the power source(s) 114 may be external to theprocessing system 104 or external to the electronic device 100.Non-limiting examples of power source(s) 114 include single-use powersources, rechargeable power sources, and/or power sources developed fromnickel-cadmium, lithium-ion, or other suitable material as well powercords and/or adapters, which are in turn connected to electrical power.

Optical sensor 102 can be implemented as part of the electronic device100, or can be physically separate from the electronic device 100. Asappropriate, the optical sensor 102 may communicate with parts of theelectronic device 100 using any one or more of the following: buses,networks, and other wired or wireless interconnection and communicationtechnologies. Examples technologies may include Inter-Integrated Circuit(I²C), Serial Peripheral Interface (SPI), PS/2, Universal Serial bus(USB), Bluetooth®, Infrared Data Association (IrDA), and various radiofrequency (RF) communication protocols defined by the IEEE 802.11standard. In some embodiments, optical sensor 102 is implemented as afingerprint sensor to capture a fingerprint image of a finger of a user.In accordance with the disclosure, the optical sensor 102 uses opticalsensing for the purpose of object imaging including imaging biometricssuch as fingerprints. The optical sensor 102 can be incorporated as partof a display, for example, or may be a discrete sensor.

Some non-limiting examples of electronic devices 100 include personalcomputing devices (e.g., desktop computers, laptop computers, netbookcomputers, tablets, web browsers, e-book readers, and personal digitalassistants (PDAs)), composite input devices (e.g., physical keyboards,joysticks, and key switches), data input devices (e.g., remote controlsand mice), data output devices (e.g., display screens and printers),remote terminals, kiosks, video game machines (e.g., video gameconsoles, portable gaming devices, and the like), communication devices(e.g., cellular phones, such as smart phones), and media devices (e.g.,recorders, editors, and players such as televisions, set-top boxes,music players, digital photo frames, and digital cameras).

In some embodiments, the optical sensor 102 may provide illumination tothe sensing region. Reflections from the sensing region in theillumination wavelength(s) are detected to determine input informationcorresponding to the input object.

The optical sensor 102 may utilize principles of direct illumination ofthe input object, which may or may not be in contact with a sensingsurface of the sensing region depending on the configuration. One ormore light sources and/or light guiding structures may be used to directlight to the sensing region. When an input object is present, this lightis reflected from surfaces of the input object, which reflections can bedetected by the optical sensing elements and used to determineinformation about the input object.

The optical sensor 102 may also utilize principles of internalreflection to detect input objects in contact with a sensing surface.One or more light sources may be used to direct light in a light guidingelement at an angle at which it is internally reflected at the sensingsurface of the sensing region, due to different refractive indices atopposing sides of the boundary defined by the sensing surface. Contactof the sensing surface by the input object causes the refractive indexto change across this boundary, which alters the internal reflectioncharacteristics at the sensing surface, causing light reflected from theinput object to be weaker at portions where it is in contact with thesensing surface. Higher contrast signals may be achieved usingfrustrated total internal reflection (FTIR) to detect the input object.In such embodiments, the light may be directed to the sensing surface atan angle of incidence at which it is totally internally reflected,except where the input object is in contact with the sensing surface andcauses the light to partially transmit across this interface. An exampleof this is presence of a finger introduced to an input surface definedby a glass to air interface. The higher refractive index of human skincompared to air causes light incident at the sensing surface at thecritical angle of the interface to air to be partially transmittedthrough the finger, where it would otherwise be totally internallyreflected at the glass to air interface. This optical response can bedetected by the system and used to determine spatial information. Insome embodiments, this can be used to image small scale fingerprintfeatures, where the internal reflectivity of the incident light differsdepending on whether a ridge or valley is in contact with that portionof the sensing surface.

FIG. 2 illustrates an example of an electronic device 116, such as amobile phone, which includes a cover layer, such as cover glass 118,over a display 120. The disclosed method and system may be implementedsuch that the display 120 includes an optical sensor to image an inputobject. Alternatively, a separate discrete component 122 may include anoptical sensor that provides the optical sensing capabilities. Adiscrete component 122 may provide more flexibility in designing theoptical components of the sensor for optimum illumination and/or signalconditioning than when attempting to integrate the optical sensorcomponents on a display substrate, such as a thin film transistor (TFT)backplane. In one embodiment, the discrete component 122 is not locatedbeneath the display 120, as shown in FIG. 2. In another embodiment, thediscrete component 122 is located beneath the display 120.

FIG. 3 depicts an optical sensor 102 in accordance with some embodimentsof the disclosure. The optical sensor 102 is generally configured in anoptical system that measures a physical characteristic by detectingelectromagnetic radiation. The optical sensor 102 includes one or morelight source(s) 302 for illuminating a sensing region 304 and one ormore light detector(s) 306 for detecting light from the sensing region304. When operated, the light source(s) 302 provide emitted light 308 tothe sensing region 304, and the emitted light 308 interacts withobject(s) 310 when the object(s) 310 are in or near the sensing region304. The light detector(s) 306 detect received light 312 from thesensing region 304 and convert the received light 312 into input data314.

The sensing region 304 shown in FIG. 3 generally comprises a region fromwhich the optical sensor 102 is configured to sense input information.More specifically, the sensing region 304 comprises one or more spacesor areas in which the object(s) 310 can be positioned (in whole or inpart) and detected by the optical sensor 102. The sensing region 304 iscoupled optically to the light source(s) 302 to provide one or moreillumination paths 316 for the emitted light 308 to reach the sensingregion 304 from the light source(s) 302. The sensing region 304 is alsocoupled optically to the light detector(s) 306 to provide one or moredetection path(s) 318 for the received light 312 to reach the lightdetector(s) 306 from the sensing region 304. The illumination path(s)316 and the detection path(s) 318 may include physically separateoptical paths or optical paths that may intersect or overlap (in wholeor in part). Some embodiments of the sensing region 304 include athree-dimensional space encompassing a portion of the environment thatis within a suitable depth or range of the light source(s) 302 and thelight detector(s) 306 for depth imaging or proximity sensing. Someembodiments of the sensing region 304 include an input surface (e.g., asensor plate) having an area for receiving contact of the object(s) 310for contact imaging or touch sensing.

The light source(s) 302 may include one or more light emitting diodes(LEDs), lasers, electroluminescent devices, or other light emittersconfigured to illuminate the sensing region 304 for object detection.Some embodiments of the light source(s) 302 include electroniccomponents that comprise organic or inorganic materials that may beelectronically controlled or operated. In some embodiments, the lightsource(s) 302 includes a plurality of light sources that may be arrangedin a regular array or irregular pattern, and further, the plurality oflight sources may be physically located together or spatially segregatedin two or more separate locations. The light source(s) 302 may emit oneor more wavelengths of light in the visible or invisible spectrum. Someembodiments of the light source(s) 302 emit light in a narrow band, abroad band, or multiple different bands. In some embodiments, the lightsource(s) 302 includes one or more dedicated light emitters that areused only for illuminating the sensing region 304 for object detection.In some embodiments, the light source(s) 302 includes one more lightemitters associated with one or more other functions of an electronicsystem, such as displaying visual information or images to a user.

The light detector(s) 306 may include one or more photodiodes (PDs),charge coupled devices (CCDs), phototransistors, photoresistors, orother photosensors configured to detect light from the sensing region304 for object detection. The light detector(s) 306 may include organicor inorganic materials and which may be electronically measured oroperated. In some embodiments, the light detector(s) 306 includes aplurality of light detectors, which may be arranged in a regular arrayor irregular pattern and may be physically located together or spatiallysegregated in two or more separate locations. In some embodiments, thelight detector(s) 306 includes one or more image sensors, which may beformed using a complementary metal-oxide-semiconductor (CMOS) or a thinfilm transistor (TFT) process. The light detector(s) 306 may detectlight in a narrow band, a broad band, or multiple different bands, whichmay have one or more wavelengths in the visible or invisible spectrum.The light detector(s) 306 may be sensitive to all or a portion of theband(s) of light emitted by the light source(s) 302.

The object(s) 310 includes one or more animate or inanimate objects thatprovide input information that is of interest to the optical sensor 102.In some embodiments, the object(s) 310 includes one or more persons,fingers, eyes, faces, hands, or styluses. When the object(s) 310 ispositioned in the sensing region 304, all or a portion of the emittedlight 308 may interact with the object(s) 310, and all or a portion ofthe emitted light 308 may be reach to the light detector(s) 306 asreceived light 312. The received light 312 may contain effectscorresponding to the interaction of the emitted light 308 with theobject(s) 310. In some embodiments, the interaction of the emitted light308 includes reflection, refraction, absorption, or scattering by theobject(s) 310. In some embodiments, the received light 312 includeslight reflected, refracted, or scattered by the object(s) 310 or one ormore surfaces of the sensing region 304.

The light detector(s) 306 convert all or a portion of the detected lightinto input data 314 containing information associated with the object(s)310. The input data 314 may include one or more electronic signals orimages containing input information, such as positional information,spectral information, temporal information, spatial information,biometric information, or image information. The optical sensor 102 mayprovide or transmit the input data 314 to one or more processingcomponents or processing systems (such as, for example, processingsystem 104 in FIG. 1) for storage or further processing.

Components of the optical sensor 102 may be contained in the samephysical assembly or may be physically separate. For example, the lightsource(s) 302, the light detector(s) 306, or sub-components thereof maybe contained in the same semiconductor package or same device housing.Alternatively, the light source(s) 302, the light detector(s) 306, orsub-components thereof may be contained in two or more separate packagesor device housings. Also, some components of the optical sensor 102,such as the object(s) 310 and the sensing region 304, may or may not beincluded as part of a physical assembly of the optical sensor 102. Insome embodiments, the object(s) 310 is provided by one or more users orenvironments during operation of the optical sensor 102. In someembodiments, the sensing region 304 includes a structural input surfaceor housing included with a physical assembly of the optical sensor 102.In some embodiments, the sensing region 304 includes an environmentalspace associated with the optical sensor 102 during its operation.Further, in some embodiments one or more additional optical components(not pictured) are included to act on the light in the optical sensor102. For example, one or more light guides, lenses, mirrors, refractiveelements, diffractive elements, spatial filters, spectral filters,polarizers, collimators, or pinholes may be included in the illuminationpath(s) 316 or detection path(s) 318 to modify or direct the light asappropriate for detection of the object(s) 310. In some embodiments, oneor more angled spatial filters or angled collimators (e.g., angledoptical fibers, offset aperture stacks, offset microlenses, etc.) may bedisposed in the illumination path(s) 316 or detection path(s) 318 tocontrol a direction of the emitted light 308 or the received light 312.

Some under-OLED sensors suffer from poor signal-to-noise ratio (SNR),e.g., ˜5:1, which can result in poor fingerprint sensing performance,especially with dry fingers. Some of the disclosed embodiments provide asensing system with improved SNR.

FIG. 4 depicts example reflectance in an optical fingerprint sensor, inaccordance with some embodiments. As shown, a finger 402 is placed onglass 406. Interface 404 provides a sensing surface for the finger 402to be placed on the glass 406. The finger 402 includes ridges 410 andvalley 412.

In the example shown in FIG. 4, the glass 406 has refractive index n₁,the finger 402 has refractive index n₂, and an air gap 408 formed by thevalley 412 has refractive index n₀. The refractive index of the skin offinger 402 can vary from person to person and depends on lightfrequency, but some typical ranges are between approximately 1.37 and1.50. Referring to FIG. 4, ridge reflectance (R_(Ridge)) between glass406 and ridges 410 and valley reflectance (R_(Valley)) between glass 406and valley 412 are different. The difference (i.e.,R_(Ridge)−R_(Valley)) is referred to as “ridge/valley contrast,” and iswhat allows the optical fingerprint sensor to differentiate betweenridges 410 and valleys 412 of the finger 402. A higher ridge/valleycontrast can improve optical fingerprint sensing performance.

The ridge reflectance R_(Ridge) and valley reflectance R_(Valley) we aregoverned by the Fresnel equations and are dependent on the polarizationof the incident light 414.

For s-polarized light, the reflectance (R_(S)) between glass 406 andridge 410 is governed by the equation:

$\begin{matrix}{R_{S} = \left\lbrack \frac{n_{1^{*}{\cos{(\theta)}}} - {n_{2^{*}}\sqrt{1 - \left( {\frac{n_{1}}{n_{2}}{\sin(\theta)}} \right)^{2}}}}{n_{1^{*}{\cos{(\theta)}}} + {n_{2^{*}}\sqrt{1 - \left( {\frac{n_{1}}{n_{2}}{\sin(\theta)}} \right)^{2}}}} \right\rbrack^{2}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$

For p-polarized light, the reflectance (R_(P)) between glass 406 andridge 410 is governed by the equation:

$\begin{matrix}{R_{P} = \left\lbrack \frac{{n_{1^{*}}\sqrt{1 - \left( {\frac{n_{1}}{n_{2}}{\sin(\theta)}} \right)^{2}}} - n_{2^{*}{\cos{(\theta)}}}}{n_{1^{*}}\sqrt{1 - \left( {\frac{n_{1}}{n_{2}}{\sin(\theta)}} \right)^{2} + n_{2^{*}{\cos{(\theta)}}}}} \right\rbrack^{2}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

In the equations Eq. 1-2 above, theta (θ) refers to the incident anglerelative to the normal of the glass-to-ridge interface (e.g., as shownin FIG. 4). As used herein, p-polarized light has an electric fieldpolarized parallel to the plane of incidence, and an electric field ofs-polarized light is perpendicular to the plane of incidence.

The reflectance (R) for non-polarized light between glass 406 and ridge410 is governed by the equation:

$\begin{matrix}{R = {\frac{1}{2}\left( {R_{S} + R_{P}} \right)}} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

For the reflectance values between glass 406 and valley 412, therefractive index n₂ for skin is replaced with the refractive index n₀for air in the equations (Eq. 1-3) above.

FIG. 5 is a graph illustrating example valley reflectance R_(Valley)plotted against incident angle (θ) of incoming light, according to oneembodiment. In the example shown in FIG. 5, the refractive index ofglass (n_(glass)) is 1.50, and the refractive index of the air gap ofthe valley is 1.0. The refractive index of glass (n_(glass)) of 1.50 isused throughout the disclosure as an example, although other transparentmaterials with different refractive indices are also within the score ofthe disclosure. Curve 502 represents valley reflectance R_(Valley) fors-polarized light. Curve 504 represents valley reflectance R_(Valley)for p-polarized light. As shown, the valley reflectance R_(Valley)increases dramatically just before reaching full reflection (i.e., totalinternal reflection) at an angle around 40 degrees for both s-polarizedlight and p-polarized light.

FIG. 6 is a graph illustrating example ridge reflectance R_(Ridge)plotted against incident angle (θ) of incoming light, according to oneembodiment. In the example in FIG. 6, the refractive index of glass(n_(glass)) is 1.50, and the refractive index of finger skin (n_(skin))of the ridge is 1.37. As indicated above, the refractive index of fingerskin can vary from person to person and depend on light frequency, butsome typical ranges are between approximately 1.37 and 1.50. Curve 602represents ridge reflectance R_(Ridge) for s-polarized light. Curve 604represents ridge reflectance R_(Ridge) for p-polarized light. As shown,the ridge reflectance R_(Ridge) increases dramatically just beforereaching full reflection (i.e., total internal reflection) at an anglearound 65 degrees for both s-polarized light and p-polarized light.

As can be seen by comparing the plots in FIG. 5 and FIG. 6, fullreflection begins at different incident angles for valleys (i.e.,approximately 40 degrees) and ridges (i.e., approximately 65 degrees).By subtracting the plots in FIG. 6 from the plots in FIG. 5, aridge/valley contrast can be determined.

FIG. 7 is a graph illustrating example ridge/valley contrast, accordingto one embodiment. In the example in FIG. 7, the refractive index ofglass (n_(glass)) is 1.50; the refractive index of finger skin(n_(skin)) is 1.37; and the refractive index of air (n_(air)) is 1.00.Curve 702 represents ridge/valley contrast for s-polarized light. Curve704 represents ridge ridge/valley contrast for p-polarized light. Asshown in the graph, at an incident angle of 0 degrees (i.e., verticallight, parallel to the normal of the input surface), the ridge/valleycontrast is just 3.795%. By contrast, at an incident angle of 50degrees, the ridge/valley contrast is 98.37%. As such, the signal thatdifferentiates between ridge and valley can be improved by about 20times (20×) with an optimized incident angle. In the example shown inFIG. 7, an optimized incident angle is approximately 42 degrees toapproximately 65 degrees.

FIG. 8 is another graph illustrating example ridge/valley contrast,according to one embodiment. In the example in FIG. 8, refractive indexof glass (n_(glass)) is 1.50; refractive index of finger skin (n_(skin))is 1.50; and refractive index of air (n_(air)) is 1.00. Curve 802represents ridge/valley contrast for s-polarized light. Curve 804represents ridge ridge/valley contrast for p-polarized light. As shownin the graph, at an incident angle of 0 degrees, the ridge/valleycontrast is just 4%. By contrast, at an incident angle of 47 degrees,the ridge/valley contrast is 100%. In the example shown in FIG. 8, anoptimized incident angle to improve ridge/valley contrast isapproximately 42 degrees to approximately 88 degrees.

FIG. 9A illustrates an example of a stack-up for an optical sensordevice 200 used to image an input object 216, such as a fingerprint. Theoptical sensor device 200 includes an image sensor array 202, acollimator filter layer (or light conditioning layer) 204 disposed abovethe image sensor array 202, an illumination layer 207 disposed above thecollimator filter layer 204, a light source 208, and a cover layer 210.In certain embodiments, a blocking layer 214 may also be provided.

The cover layer 210 protects the inner components of the optical sensordevice 200, such as the image sensor array 202. The cover layer 210 mayinclude a cover glass or cover lens that protects inner components of adisplay in addition to the optical sensor device 200. A sensing regionfor the input object is defined above the cover layer 210. A sensingsurface 218 (i.e., top surface) of the cover layer 210 provides acontact area for the input object 216 (e.g., fingerprint). The coverlayer 210 may be made of any transparent material such as glass,transparent polymeric materials and the like.

Although generally described in the context of a fingerprint forillustrative purposes, the input object 216 can be any object to beimaged. Generally, the input object 216 will have various features. Byway of example, when the input object 216 is a fingerprint, it hasridges and valleys. Due to their protruding nature, the ridges contactthe sensing surface 218 of the cover layer 210. In contrast, the valleysdo not contact the sensing surface 218 and instead form an air gapbetween the input object 216 and the sensing surface 218. The inputobject 216 may have other features such as a stain, ink, moisture andthe like that do not create significant structural differences inportions of the input object 216, but which may affect its opticalproperties. The methods and systems disclosed herein are suitable forimaging such structural and non-structural features of the input object216.

The illumination layer 207 includes a light source 208 and/or a lightguiding element 206 that directs illumination to the sensing region inorder to image the input object. As shown in FIG. 9A, the light source208 transmits beams or rays of light 212 into the light guiding element206 and the transmitted light propagates through the light guidingelement 206. The light guiding element 206 may utilize total internalreflection, or may include reflecting surfaces that extract light uptowards the sensing region. Some of the light in the illumination layermay become incident at the sensing surface 218 in an area that iscontact with the input object 216. The incident light is in turnreflected back towards the collimator filter layer 204. In the exampleshown, the light source 208 is disposed adjacent to the light guidingelement 206. However, it will be understood that the light source 208may be positioned anywhere within the optical sensor device 200 providedthat emitted light reaches the light guiding element 206. For example,the light source 208 may be disposed below the image sensor array 202.Moreover, it will be understood that a separate light guiding element206 is not required. For example, the light transmitted from the lightsource 208 can be transmitted directly into the cover layer 210 in whichcase the cover layer 210 also serves as a light guiding element. Asanother example, the light transmitted from the light source 208 can betransmitted directly to the sensing region, in which case the lightsource 208 itself serves as the illumination layer.

The light provided by the illumination layer 207 to image the inputobject 216 may be in the near infrared (NIR) or visible spectrum. Thelight can have a narrow band of wavelengths, a broad band ofwavelengths, or operate in several bands.

The image sensor array 202 detects light passing through the collimatorfilter layer 204. Examples of suitable image sensor arrays 202 arecomplementary metal oxide semiconductor (CMOS) and charge coupled device(CCD) sensor arrays. The image sensor array 202 includes a plurality ofindividual optical sensing elements capable of detecting the intensityof incident light. In some embodiments, the image sensor array 202 isformed in a silicon sensor substrate. In other embodiments, the imagesensor array 202 is formed on a glass thin film transistor substrate.

To achieve optical sensing of fingerprints and fingerprint-sizedfeatures through thicker cover layers 210, light reflected from theinput object 216 may be conditioned by the collimator filter layer 204so that the light reaching a sensing element in the image sensor array202 comes from a small spot on the input object 216 directly or nearlydirectly above the sensor element. The conditioning can decrease imageblurring contributed by unwanted light, e.g., those arriving at asensing element from an object far away from the optical sensingelements.

In one embodiment, the collimator filter layer 204 is provided with anarray of apertures, or collimator holes, 220. Each aperture or hole maybe directly above one or more optical sensing elements on the imagesensor array 202. In some embodiments, a plurality of apertures (clusterof apertures) may be above a single optical sensing element (also calledan imaging cell) with the single optical sensing element comprising, forexample, a single photosensor or multiple photosensors combined into asingle pixel. The apertures 220 may be formed using any suitabletechnique, such as laser drilling, etching, and the like. The collimatorapertures or holes 220 may form an array of any suitable regular orirregular pattern.

In FIG. 9A, the collimator filter layer 204 allows light rays reflectedfrom the input object 216 (e.g., finger) at normal or near normalincidence to the collimator filter layer 204 to pass and reach theoptical sensing elements of the image sensor array 202. In oneembodiment, the collimator filter layer 204 is an opaque layer witharray of holes 220. The collimator filter layer 204 may be laminated,stacked, or built directly above the image sensor array 202. By way ofexample, the collimator filter layer 204 may be made of a plasticmaterial such as polycarbonate, PET, polyimide, carbon black, inorganicinsulating or metallic materials, silicon, or SU-8. In certainembodiments, the collimator filter layer 204 is monolithic.

An optional blocking layer 214 may be a part of optical sensor device200. The blocking layer 214 may be a semitransparent or opaque layer andmay be disposed above the collimator filter layer 204. For example, theblocking layer 204 may be disposed between the cover layer 210 and theillumination layer 207, as shown in FIG. 9A. Alternatively, the blockinglayer 214 may be disposed between the illumination layer 207 and thecollimator filter layer 204. The blocking layer 214 may be configured toobscure ambient light illumination from reaching the image sensor array202, while still allowing the optical sensor device 200 to operate. Theblocking layer 214 may include a number of different materials orsub-layers. For example, a thin metal or electron conducting layer maybe used where the layer thickness is less than the skin depth of lightpenetration in the visible spectrum. Alternatively, the blocking layer214 may include a dye and/or pigment or several dyes and/or pigmentsthat absorb light, for example, in the visible spectrum. As yet anotheralternative, the blocking layer 214 may include several sub-layers ornano-sized features configured to cause interference with certainwavelengths, such as visible light for example, so as to selectivelyabsorb or reflect different wavelengths of light. The light absorptionprofile of the blocking layer 214 may be formulated to give a particularappearance of color, texture, or reflective quality thereby allowing forparticular aesthetic matching or contrasting with the device into whichthe optical sensor device 200 is integrated. In some embodiments, asemitransparent material may be used with visible illuminationwavelengths to allow sufficient light to pass through the blocking layer214 to the sensing region while still sufficiently obscuring componentsbelow.

FIG. 9B illustrates another example of a stack-up for an optical sensordevice 900. The optical sensor device 900 includes an image sensor array202, a collimator filter layer (or light conditioning layer) 204disposed above the image sensor array 202, a display layer 920 disposedabove the collimator filter layer 204, and a cover layer 210. In someembodiments, an optional blocking layer 214 may also be provided. Asshown in FIG. 9B, light from the display layer 920 may be used toilluminate the input object 216 (e.g., finger). In this embodiment, adiscrete light source is not required.

The display layer 920 may comprise the display screen of an electronicdevice and may include a plurality of light sources 922. The displaylayer 920 may be any type of dynamic display capable of displaying avisual interface to a user, and may include any type of light sources922, such as light emitting diodes (LEDs), organic LEDs (OLEDs), cathoderay tube (CRT), liquid crystal display (LCD), plasma,electroluminescence (EL), or other display technology. The display layer920 may also be flexible or rigid, and may be flat, curved, or haveother geometries. In some embodiments, the display layer 920 includes aglass or plastic substrate for TFT circuitry and/or other circuitry,which may be used to provide images and/or provide other functionality.The cover layer 210 is disposed above display layer 920 and may providea sensing surface 218 for the input object 216. Example cover layer 210materials include plastic, optically clear amorphous solids, such aschemically hardened glass, as well as optically clear crystallinestructures, such as sapphire. In some embodiments, the display layer 920may comprise a polarizer, e.g., a p-polarizer or an s-polarizer. Whenreferring to polarization states, p-polarization refers to thepolarization plane parallel to the polarization axis of the polarizerbeing used. The s-polarization refers to the polarization planeperpendicular to the polarization axis of the polarizer.

When sensing input objects, e.g., sensing fingerprints orfingerprint-sized features through thicker cover layers 210, lightemitted by the light sources 922 of the display layer 920 reflected fromthe input object 216 may be conditioned by the collimator filter layer204 so that the light reaching a sensing element in the image sensorarray 202 comes from a portion of the input object 216 directly abovethe sensor element.

In FIGS. 9A-9B, collimator filter layer 204 includes vertically orientedapertures, or collimator holes, 220. As such, the collimator filterlayer 204 allows vertical or nearly vertical light (i.e., light within atolerance angle from a vertical axis) to arrive at the image sensorarray 202. In this example, the vertical axis corresponds to a normal ofthe sensing surface 218 and/or a normal of a plane of light sources 922.

FIG. 10 depicts yet another example of an optical fingerprint sensorstack-up. In this example, an image sensor array 1002 is disposed belowa display layer 1020 (e.g., below a transparent OLED display substrateand below light emitters of the OLED display). The display layer 1020 isdisposed below a transparent cover layer 1010, where a top surface ofthe cover layer 1010 provides an input surface for a finger 1016. Lightsource(s) for illuminating the input surface are disposed in the displaylayer 1020 (e.g., light emitters disposed above a transparent displaysubstrate, or OLED light emitting display pixels themselves) are used toilluminate the finger 1016. An angled collimator layer 1004 is disposedbelow the light source(s) and the display layer 1020. The image sensorarray 1002 is disposed below the angled collimator layer 1004.

The angled collimator layer 1004 includes apertures or collimator holesoriented at a non-zero angle (θ) relative to vertical, i.e., a normal ofthe input surface and/or a normal of the pixel plane. In the exampleshown, light from the display layer 1020 (e.g., light from an OLEDsub-pixel emitters) is used as light source, and the emitted light maygo in multiple directions. Please note that any wavelengths of light maybe used.

The angled collimator layer 1004 allows light 1030 that is parallel toangle θ (or within a tolerance angle of angle θ) to pass through theangled collimator layer 1004 and reach the image sensor layer 1002,while absorbing or blocking other light. By absorbing or blockingunwanted light, angled collimator may reduce SNR and thereby increaseridge/valley contrast, as described herein. In some embodiments, thedisplay layer 1020 may include a polarizer (not shown for simplicity),to further improve ridge/valley contrast.

FIG. 11A depicts an example structure and method of manufacturing anangled collimator using a fiber. The fiber may comprise a fiber bundle1100 of optical fibers. In some implementations, optical fibers includea core and a cladding surrounding the core arranged to spatially confinelight through the core using total internal reflection (e.g., therefractive index of the cladding is less than the refractive index ofthe core). In some embodiments, a light absorbing material having arefractive index similar to that of the core may be used as the cladding(e.g., black or dark colored glass). In these embodiments, lightsufficiently off-axis relative to an axis of the fiber core (i.e., leftto right in FIG. 11A) may be absorbed by the light absorbing materialrather than totally internally reflected, while light parallel to theaxis of the fibers may pass through.

To create an angled collimator similar to that shown in FIG. 10, thefiber bundle 1100 is sliced off-axis (as opposed to cutting or slicingthe fiber bundle 1100 perpendicular to the fiber axis which would resultin a cross-section of the fiber bundle 1100 shown in image 1120). Inparticular, the fiber bundle 1100 shown in FIG. 11A may be sliced alongcut lines 1102 into multiple angled collimator plates in which each ofthe plates is sliced at an angle of 90°+θ relative to an axis of thefibers (or θ relative to perpendicular from the axis of the fibers). Insome embodiments, a manufacturing tolerance can be considered whenselecting the cutting axis θ. For example, if an acceptance angle isdesired that is centered around a minimum of 41.8 degrees and maximum of55 degrees (i.e., referring to earlier calculations in FIGS. 7-8, basedon capture of light totally internally reflected by fingerprint valleys,but not ridges), then a nominal cutting axis value of 48 degrees canprovide good performance within certain margins. It should also beunderstood that if the core glass of the fiber bundle 1100 has arefractive index different from 1.5, than the optimized angle can bedifferent. A result of cutting the fiber bundle 1100 along the cuttingaxis θ is shown as image 1130.

FIG. 11B depicts a flow diagram of forming an optical element, accordingto one embodiment. At step 1112, a bundle of optical fibers is provided.An example is shown in FIG. 11A. In one embodiment, each of the fibersin the bundle of optical fibers includes a core surrounded by a lightabsorbing material. At step 1114, the bundle is sliced with a pluralityof cuts to form an angled filter. In one embodiment, each cut of theplurality of cuts is parallel to each other cut and is between 0 and 90degrees relative to an axis of the fibers. At step 1116, an opticalsensor is formed that includes the angled filter. As described herein,the angled filter may be disposed above an image sensor array. Theangled filter may be configured to allow light reflected from an inputsurface to pass through the angled filter, where the light is within atolerance angle of an acceptance angle.

FIG. 12 depicts an example structure and method of manufacturing anangled collimator using stacked aperture layers. The angled collimatorshown in FIG. 12 includes alternating transparent layers 1202 andmultiple patterned light shielding layers 1204 (shown as black lines).Each of the light shielding layers 1204 includes apertures 1206 formedin the patterned light shielding layers 1204. Apertures 1206 allow thelight 1208 at acceptance angle (θ) to pass through, while other light1210 is blocked. The alignment of apertures 1206 in the different layerscan determine the acceptance angle (θ) of the light. Instead of havingapertures 1206 that are vertically aligned with each other (which wouldresult in a vertically oriented collimator having an acceptance anglecentered around a vertical angle), the apertures 1206 are offsetrelative to each other. For example, the apertures in the bottom lightshielding layer are offset from the apertures in the light shieldinglayer immediately above the bottom light shielding layer, and so forth.This results in an acceptance angle that includes or is centered arounda non-zero angle θ, similar to that shown in FIG. 10.

FIG. 13 depicts an example structure and method of manufacturing anangled collimator using stacked aperture layers and microlenses. Similarto the design shown in FIG. 12, the design shown in FIG. 13 includesalternating transparent layers 1302 and patterned light shielding layers1304 (shown as black lines). Each of the patterned light shieldinglayers 1304 includes apertures 1306 to allow light to pass through. Theapertures 1306 in the patterned light shielding layers 1304 may bearranged to determine the acceptance angle (θ) of the light.

Microlenses 1308 (e.g., a micro lens array) may be included on atop-most transparent layer 1302 to focus light incident on themicrolenses 1308 in a certain direction, i.e., in a direction thatallows the light to pass through the apertures 1306 of the angledcollimator. For example, the microlenses 1308 may focus light fromvarious angles that would otherwise not pass through the apertures 1306,to allow the light to pass through the apertures 1306.

The transparent layers 1302 may have varying thicknesses. For example,the transparent layers 1302 may become thicker towards the bottom of thestack of transparent layers 1302 (i.e., closer to an image sensor array,which would be disposed below the angled collimator), such that thethickest transparent layer 1302 is at the bottom of the stack of layers.In other embodiments, each transparent layer 1302 has the samethickness.

In some embodiments, the patterned light shielding layers 1304 may havevarying structure such that the apertures 1306 may be of different sizes(e.g., diameters for circular apertures) for different layers in thestack of layers. Apertures of varying sizes may improve the transmissionof light through the collimator. For example, the apertures 1306 maybecome smaller towards the bottom of the stack of layers (i.e., closerto the image sensor array), such that the smallest apertures 1306 arefound at the bottom-most layer of the stack of layers. In otherembodiments, the apertures 1306 at each layer may have the same size.

In some implementations, the microlenses 1308 above the collimator maycause the light output from the microlenses 1308 to take the shape of acone. In such embodiments, by sizing the apertures 1306 differently fordifferent layers in the stack of layers such that the smallest apertures1306 are found at the bottom-most layer, more light may pass through thecollimator as compared with sizing the apertures the same for each layerin the stack of layers.

FIGS. 10-13 have generally been described with reference to angledcollimators that are disposed underneath a display layer (e.g., OLEDdisplay) and between the display layer and an image sensor array, wherethe angled collimators control an angle from which the image sensorarray accepts light. In some alternate embodiments, a similar imagesensor array can be used outside of a display area. In still furtherembodiments, the angle of illumination can be controlled.

FIGS. 14A-14B show examples in which an angular filter (such as one ofthe angled collimators described above) can be used outside of a displayarea in connection with a discrete light source for illuminating thesensing region, according to various embodiments.

In FIG. 14A, a cover layer 1406 is disposed on top of a collimator layer1404A, which is disposed on top of an image sensor array 1402. The imagesensor array 1402 may be disposed within a display area (not shown) ofthe device. Light from a light source 1410 that is placed outside thedisplay area is directed towards a sensing surface (e.g., top of thecover layer 1406). A finger 1408 can be placed on the sensing surfaceand detected by sensor components of the image sensor array 1402. Asshown in FIG. 14A, the collimator layer 1404A comprises an angledcollimator formed using a single layer (e.g., see collimator formedusing a fiber bundle in FIG. 11A). The collimator layer 1404A allowsincident light at a certain angle (within a tolerance) to pass throughthe collimator layer 1404A, and incident light of other angles isblocked.

In FIG. 14B, a cover layer 1406 is disposed on top of a collimator layer1404B, which is disposed on top of an image sensor array 1402. The imagesensor array 1402 may be disposed within a display area (not shown) ofthe device. Light from a light source 1410 that is placed outside thedisplay area is directed towards a sensing surface (e.g., top of thecover layer 1406). A finger 1408 can be placed on the sensing surfaceand detected by sensor components of the image sensor array 1402. Asshown in FIG. 14B, the collimator layer 1404B comprises an angledcollimator formed using multiple layers (e.g., see collimators formedusing stacked layers in FIGS. 12-13). The collimator layer 1404B allowsincident light at a certain angle (within a tolerance) to pass throughthe collimator layer 1404B, and incident light of other angles isblocked.

FIG. 15 shows an example in which an angular filter (such as one of theangled collimators described above) can be used to generate a collimatedbacklight for illuminating a sensing region, according to oneembodiment. As shown, a cover layer 1506 is disposed on top of asensor/display layer 1504, which is disposed on top of a collimatedbacklight layer 1502. The collimated backlight layer 1502 includes acollimating filter 1520 stacked on top of a light source 1510. A finger1508 can be placed on an input surface (i.e., top of the cover layer1506) and detected by sensor components of the sensor/display layer1504.

In FIG. 15, instead of using an angled collimator in the detectionoptical path (e.g., between the input surface for the finger 1508 andthe image sensor), the angled collimator is disposed in the illuminationoptical path (e.g., between the light source 1510 and the input surfacefor the finger 1508). Compared to the example shown in FIG. 10, thepositioning of the light source 1510 for illuminating the finger 1508input surface and the positioning of the image sensor for capturing thelight returning from the finger 1508 input surface are inverted in thestackup. Thus, the photosensors for capturing the fingerprint aredisposed in the display (e.g., TFT photodiodes or phototransistorsformed in an OLED display backplane), the angular filter is disposedbelow the display (e.g., below a transparent substrate of an OLEDdisplay), and a light source 1510 is provided below the collimatingfilter 1520. In this example, the collimated backlight layer 1502 mayfurther include a brightness enhancement film at the desiredillumination angle θ. The brightness enhancement film can be based onmicro-prisms or multilayer reflective polarizers, for example. Thebrightness enhancement film can be disposed between the collimatingfilter 1520 and the light source 1510.

In some implementations, a protection layer such as a protective film ora screen protector may be placed on top of the cover layer of anelectronic device. FIG. 16 depicts an embodiment in which a protectivelayer 1600, e.g., screen protection film 1600, is included over a coverlayer 1010, providing a protective barrier from scratching or breakingto cover layer 1010. In the example of FIG. 16, an image sensor array1002 is disposed below a display layer 1020 (e.g., below a transparentOLED display substrate and below light emitters of the OLED display).The display layer 1020 is disposed below the cover layer 1010. Aprotection film 1600 is placed on top of the cover layer 1010, where atop surface of the protection film 1600 provides an input surface for aninput object 1016, e.g., a finger. Light source(s) for illuminating theinput surface are disposed in the display layer 1020 (e.g., lightemitters disposed above a transparent display substrate, or OLED lightemitting display pixels themselves, are used to illuminate the finger1016). An angled collimator layer 1004 is disposed below the lightsource(s) and the display layer 1020. The image sensor array 1002 isdisposed below the angled collimator layer 1004.

As shown, light 1602 from the light source(s) travels through the coverlayer 1010 towards finger 1016 and is refracted by the protection film1600 as refracted light 1604. The refracted light 1604 reflects from thesensing surface as reflected light 1606. The reflected light 1606 isrefracted again by the protection film 1600 and exits the protectionfilm 1600 as light 1608. Light 1608 travels through the cover layer 1010at an angle (θ) such that it passes through the angled collimator layer1004. In some embodiments, a refractive index (n_(film)) of theprotection film 1600 may be different than the refractive index(n_(glass)) of the cover layer 1010. In some embodiments, the refractiveindex (n_(film)) of the protection film 1600 is the same as therefractive index (n_(glass)) of the cover layer 1010.

Based on the Fresnel equations, the valley reflectance R_(Valley) andridge reflectance R_(Ridge) from the finger 1016 in FIG. 16 aredependent on the refractive index (n_(glass)) of the cover layer 1010,the refractive index (n_(film)) of the protection film 1600, therefractive index (n_(skin)) of the finger 1016, and the refractive index(noir) of the air gaps of valleys of the finger 1016.

FIG. 17 is a graph illustrating example ridge/valley contrast of asensor device that includes a protection film, according to oneembodiment. In the example in FIG. 17, the refractive index of glass(n_(glass)) is 1.50, refractive index of finger skin (n_(skin)) of theridge is 1.37, refractive index of the air gap (n_(air)) of the valleyis 1.00, and the refractive index of the protection film (n_(film)) is1.40. Curve 1702 represents ridge/valley contrast for s-polarized light.Curve 1704 represents ridge ridge/valley contrast for p-polarized light.As shown in the graph, at an incident angle of 0 degrees, theridge/valley contrast is just 2.759%. By contrast, at an incident angleof 50 degrees, the ridge/valley contrast is 98.15%. As such, the signalthat differentiates between ridge and valley can be improved by ˜35times (35×) with an optimized incident angle. In the example shown inFIG. 17, such an optimized angle is approximately 42 degrees toapproximately 65 degrees.

FIG. 18 is a graph illustrating example ridge/valley contrast of asensor device that includes a protection film, according to oneembodiment. In the example in FIG. 18, the refractive index of glass(n_(glass)) is 1.50, refractive index of finger skin (n_(skin)) of theridge is 1.37, refractive index of the air gap (n_(air)) of the valleyis 1.00, and the refractive index of the protection film (n_(film)) is1.60. Curve 1802 represents ridge/valley contrast for s-polarized light.Curve 1804 represents ridge ridge/valley contrast for p-polarized light.As shown in the graph, at an incident angle of 0 degrees, theridge/valley contrast is just 4.716%. By contrast, at an incident angleof 50 degrees, the ridge/valley contrast is 95.11%. In the example shownin FIG. 18, such an optimized angle to improve ridge/valley contrast isapproximately 42 degrees to approximately 65 degrees.

As can be seen by comparing the graphs in FIGS. 17-18 (i.e., includingprotection film) with the graphs in FIG. 7 (i.e., not includingprotection film), the ridge/valley contrast loss caused by internalreflection of protection film is just a few percent; thus, goodperformance may still be achieved even when using protection film. Whenusing protection film, the waveforms are very similar to not usingprotection film, which means the same optimized acceptance angle canwork for both cases (i.e., with or without protection film).

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.,“such as”) provided herein, is intended merely to better illuminate theinvention and does not pose a limitation on the scope of the inventionunless otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element as essential to thepractice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

What is claimed is:
 1. A device for optical sensing, comprising: adisplay comprising a transparent substrate and a plurality of lightemitters disposed above the transparent substrate; a transparent coverlayer disposed above the display, wherein a top surface of thetransparent cover layer provides an input surface for sensing an inputobject; an angled filter disposed below the transparent substrate of thedisplay, wherein the angled filter is configured to allow light within atolerance angle of an acceptance angle to pass through the angledfilter, wherein the acceptance angle is centered around a non-zero anglerelative to a normal of the input surface; and a plurality ofmicrolenses disposed at a top surface of the angled filter andconfigured to focus light through the angled filter towards an imagesensor disposed below the angled filter, wherein the non-zero angle isbetween a first angle corresponding to total internal reflection at aninterface between the input surface and a first substance and a secondangle corresponding to total internal reflection at an interface betweenthe input surface and a second substance.
 2. The device of claim 1,wherein the input object comprises a finger, and the first substancecomprises air and the second substance comprises a fingerprint ridge ofthe finger.
 3. The device of claim 1, wherein the angled filter furthercomprises a fiber oriented at the non-zero angle.
 4. The device of claim1, wherein the angled filter further comprises a plurality oftransparent layers and a plurality of light shielding layers, whereineach of the light shielding layers includes apertures configured toallow light at the non-zero angle to pass through the angled filter. 5.The device of claim 4, wherein a first light shielding layer of theplurality of light shielding layers comprises apertures having a firstdiameter, and wherein a second light shielding layer of the plurality oflight shielding layers comprises apertures having a different seconddiameter.
 6. The device of claim 4, wherein a first transparent layer ofthe plurality of plurality of transparent layers has a first thickness,and wherein a second transparent layer of the plurality of plurality oftransparent layers has a different second thickness.
 7. The device ofclaim 1, wherein the input object comprises a finger, and the imagesensor is configured to capture a fingerprint image of the finger basedon illumination of the input surface by the plurality of light emittersin the display.
 8. The device of claim 1, wherein the display comprisesan organic light emitting diode (OLED) display.
 9. An optical sensor,comprising: an image sensor array comprising a plurality of pixels; andan angled filter disposed above the image sensor array, the angledfilter comprising a plurality of light collimating apertures and lightblocking material, wherein the angled filter is configured to allowlight reflected from an input surface towards the image sensor arraythat is within a tolerance angle of an acceptance angle to pass throughthe angled filter, wherein the acceptance angle is centered around anon-zero angle relative to a normal of the input surface, wherein thenon-zero angle is between a first angle corresponding to total internalreflection at an interface between the input surface and a firstsubstance and a second angle corresponding to total internal reflectionat an interface between the input surface and a second substance,wherein the angled filter further comprises a plurality of transparentlayers and a plurality of light shielding layers, each of the lightshielding layers comprising apertures configured to allow light at thenon-zero angle to pass through the angled filter, wherein a first lightshielding layer of the plurality of light shielding layers comprisesapertures having a first diameter, and wherein a second lower lightshielding layer of the plurality of light shielding layers comprisesapertures having a smaller second diameter.
 10. The optical sensor ofclaim 9, wherein the first substance comprises air and the secondsubstance comprises a fingerprint ridge of a finger.
 11. The opticalsensor of claim 9, wherein the angled filter further comprises a fiberoriented at the non-zero angle.
 12. The optical sensor of claim 9,wherein a first transparent layer of the plurality of transparent layershas a first thickness, and wherein a second transparent layer of theplurality of transparent layers has a different second thickness. 13.The optical sensor of claim 9, wherein the image sensor array isconfigured to capture a fingerprint image of a finger based onillumination of the input surface by one or more light sources.
 14. Theoptical sensor of claim 13, further comprising a plurality ofmicrolenses disposed at a top surface of the angled filter andconfigured to focus light through the angled filter towards the imagesensor array.
 15. An electronic device, comprising: the device foroptical sensing of claim 1; and a processing system in operativecommunication with the device of optical sensing.
 16. The electronicdevice of claim 15, wherein the processing system comprises a processorand a memory.
 17. An electronic device, comprising: the optical sensorof claim 9; and a processing system in operative communication with theoptical sensor.
 18. The device of claim 1, wherein the angled filterfurther comprises a plurality of transparent layers and a plurality oflight shielding layers, each of the light shielding layers comprisingapertures configured to allow light at the non-zero angle to passthrough the angled filter, wherein a first light shielding layer of theplurality of light shielding layers comprises apertures having a firstdiameter, and wherein a second lower light shielding layer of theplurality of light shielding layers comprises apertures having a smallersecond diameter.
 19. The optical sensor of claim 9, wherein a firsttransparent layer of the plurality of transparent layers has a firstthickness, and wherein a second lower transparent layer of the pluralityof transparent layers has a greater second thickness.